Many semiconductor devices, for example, memory and other semiconductor devices, typically include adjacent co-planar conductors. The conductors are separated from one another by an insulating material to prevent shorts and minimize crosstalk. The insulating material should provide, among other things, low leakage currents, good mechanical strength, and low permittivity. A low permittivity insulator reduces parasitic capacitance between conductors. Since parasitic capacitance increases noise coupling and signal crosstalk between conductors, increases power consumption, slows circuit operation, and potentially introduces timing faults, the parasitic capacitance associated with insulating isolation should be minimized.
Conventional semiconductor devices often use silicon dioxide, and other materials, as an insulating material between adjacent conductors. Insulating material is deposited over the conductors so that the spaces between adjacent co-planar conductors are completely filled by the insulating material. Alternatively, trenches, which are filled with conductive material forming the conductors, may be formed in the insulating material. Often the same insulating material is also provided over the conductors as well.
Air-gaps are also thought to be good insulators between adjacent conductors because air is a relatively good dielectric. Previously, air-gaps have been formed by providing a conformal thin insulator film around a conductor, but this has problems with poor step coverage. It has been suggested that air-gaps between adjacent conductors may be formed by burning off a material between adjacent conductors to leave air-gaps. Burning refers to the process of converting a solid into a gas that can then easily diffuse out of the material of interest. The efficacy of burning material, however, has not yet been shown. Further, deposition methods with non-conformal characteristics, commonly referred to as bread loaf-like, still deposit some amount of dielectric on the sidewalls and bottom of the gap. This reduces the cross-sectional area of the air-gap. Alternative methods for forming such air-gaps between adjacent conductors are therefore desirable.